1. Field of the Invention
The present invention relates to a three-dimensional fabric, and more particularly to a three-dimensional fabric suitable for use as a frame member of a composite that is to be coupled to another member.
2. Description of the Related Art
Composite materials having a three-dimensional fabric that includes three kinds of threads are expected to be widely used as structural materials for rockets, aircraft, automobiles, marine vessels and buildings. Such fabrics include a multiplicity of warp strings extended in multiple columns and rows. Vertical threads and wefts are then woven perpendicularly in between various columns and rows of the warp strings. The fabric is used as a core and impregnated with matrix of a resin or an inorganic substance. To widely use composites of this type, it is necessary that individual members can be coupled together like general metal structural materials.
One conventional composite material has a frame composed of multiple laminated cloths. Conventionally, to couple such frame members, a hole is bored in a composite 60. A metal bushing 61 is inserted in that hole, and this composite 60 is coupled to another composite 60 or another structural member 62 by means of a bolt 63 and a nut 64, as shown in FIG. 20. In the case where composites employing a three-dimensional fabric as the frame member are coupled together by means of a bolt and a nut or a pin, it has likewise been conventionally necessary to form a hole in each composite and insert a metal bushing in the hole.
A similar approach could be used when three-dimensional fabrics are used as the frame material. That is, a hole 65 may be formed in the composite to receive a metal bushing. However, this requires actually cutting the yarns that constitute the portion of the three-dimensional fabric F that corresponds to the hole 65, as shown in FIG. 21. This reduces the strength of that portion (specially the strength against the force in the direction of the arrow). Accordingly, the length L and width W of that portion must be relatively large in order to increase the strength of the cut portion. This increases the volume of the portion surrounding the metal bushing 61, which is undesirable. Further, the hole 65 is typically bored after forming the composite. Therefore, minute cracks or the like may occur in the fabric depending on how the hole is finished. These minute cracks may damage the composite due to the concentration of stress. It is therefore difficult to predict the strength of the coupling portion in the stage of designing of the three-dimensional fabric.
In the case where a three-dimensional fabric comprises only the threads (fibers) extending in the three perpendicular axes of X, Y and Z, composites using this three-dimensional fabric as the frame member are strong enough against tensile loads acting in the individual directions. Since there are no fibers in an inclined direction to the lengthwise direction of the fabric, however, the amount of deformation of the three-dimensional fabric caused by the force acting in the inclined direction with respect to the axial direction is great. The three-dimensional fabric therefore tends to become weaker against the compressive loads than the tensile loads.